Since most states don't require registration, and there is no federal law requiring registration, most of the handguns in the U.S. are unregistered. "Unregistered" is a misleading term. It implies that a person has failed to do something that is required.
Impossible to answer without knowing what you mean by illegal handguns.
Depends on the firearm, and the laws where you are. We can't begin to give you a real answer without more info. In MOST of the US, there IS no registration of ordinary rifles, shotguns, and handguns.
PA doesn't require registration ofordinary Title I firearms, to include handguns.
That is a very difficult question to answer for a couple of reason. Only a few states require handgun registration, and there is no federal gun registration. In the few states that do require handgun registration, the information is not generally available to the public.
Rifles and shotguns, yes. Handguns, no, you must be 21 to legally purchase a handgun.
No one source of information.
Laws vary from state to state. In MOST states, there is no "registration" of firearms as such. If you live in a state that DOES require registration, then yes, that would be illegal.
Wisconsin does not require registration of handguns. Information for you: http://crime.about.com/od/gunlawsbystate/a/gunlaws_wi.htm MOST states do not require registration of firearms.
There are millions every year.
No exact answer, as there is no exact record- a good estimate is about 120 million privately owned handguns in the US.
No
Yes, they are.